Many optical elements display a property known as diattenuation, whereby the intensity transmittance of a beam that exits an optical element or sample is a function of the polarization state of the incident beam. The intensity transmittance is a maximum Tmax for one polarization state of the incident beam, and a minimum Tmin for the orthogonal polarization state for that beam.
Linear diattenuation needs two parameters to describe it: (1) angle θ which is the angle of the maximum transmission axis for linearly polarized light; and (2) magnitude Ld, which is defined as (Tmax−Tmin)/(Tmax+Tmin).
What follows is a description of a system for measuring, in addition to linear birefringence of an optical element, the linear and circular diattenuation properties of that element.